The invention relates to methods and apparatus for monitoring characteristics of a flow stream in a pipeline, in particular to dual chamber orifice fittings. More precisely, the embodiments of the invention relate to an improved valve design for a dual chamber orifice fitting.
In pipeline operations and other industrial applications, flow meters are used to measure the volumetric flow rate of a gaseous or liquid flow stream moving through a piping section. Flow meters are available in many different forms. One type of flow meter is an orifice meter, which includes an orifice fitting connected to the piping section. The orifice fitting serves to orient and support an orifice plate that extends across the piping section perpendicular to the direction of flow stream. The orifice plate is a thin plate that includes a circular opening, or orifice, that is positioned within the flow stream.
In operation, when the flow stream moving through the piping section reaches the orifice plate, the flow is forced through the orifice, thereby constricting the cross-sectional area of the flow. Due to the principles of continuity and conservation of energy, the velocity of the flow increases as the stream moves through the orifice. This velocity increase creates a pressure differential across the orifice plate. The measured differential pressure across the orifice plate can be used to calculate the volumetric flow rate of the flow stream moving through the piping section.
A dual chamber orifice fitting enables the orifice plate to be removed from the fitting without interrupting the flow stream moving through the piping section. In many designs, this is achieved by providing two chambers within the fitting wherein the orifice plate is in the flow stream in one chamber and out of the flow stream in the second chamber. An isolation valve is provided between the two chambers so as to prevent fluid communication between the two chambers but can be opened to allow the orifice plate to pass therethrough.
Valve designs that are more compact and require less movement for actuation potentially provide advantages both in reduced operating envelope requirements and in simplification of operation. Thus, the embodiments of the present invention are directed to valve apparatus for dual chamber orifice fittings that seek to overcome these and other limitations of the prior art.